Modern homes are being built with increasing emphasis on energy efficiency. This generally means more thermal insulation, more vapor barriers and better quality seals around windows and doors. This type of construction has given rise to the concern that ventilation may be inadequate, in light of the need for a continuous supply of fresh air and concerns about volatile byproducts of manufacturing of synthetic items. There is further concern in the many homes that use combustible fuels for heating and cooking or lighting. In addition to the psychometric comfort factors of heat and humidity and the essential need for oxygen, there are the serious health factors of carbon monoxide, smoke, and any other products of combustion deriving from these combustion process. Excess heat and humidity in an enclosed structure can also be quite destructive to the structure itself, leading to problems ranging from mildew, to insulation failure, to deterioration of the actual structure itself through attraction of insects and rot. In the case of electric stoves, there are also harmful effluents emitted as the results of the cooking process.
As of 2011, there were anywhere between 200 and 700 annual deaths attributed to residential, non-vehicle, carbon monoxide (CO) poisoning in the US. While equipment malfunctions, such as cracked heat exchangers played a role, a key factor in all of these injuries and deaths was inadequate ventilation. Roughly 10% of these casualties have been attributed to gas stoves and ovens. Low-level cases are more difficult to track, since the symptoms are similar to common cold or flu, but are likely to have a much higher occurrence. Thus, considering the impact of lost work days and reduced activity due to illness for low-level exposure, and the injury and death resulting from high level exposure, the cost to society of inadequate ventilation in conjunction with combustion appliances is substantial.
The ASME standards for gas stoves, which allow for trace amounts of CO, are based on the assumption that the stoves are vented. However, many are not and even those that are generally use a range hood with a fan that must be switched on manually. Many people do not turn these venting fans on unless there is detectable smoke or odor or if the kitchen becomes excessively hot. In other words, kitchens are often inadequately ventilated to a degree that may be a health and safety concern.
Carbon monoxide, being colorless and odorless is undetectable without some sort of sensing device. It is unlikely that CO being emitted by a cooking appliance will be detected by plug-in detectors since the installation instructions for these devices recommend placing them a minimum distance away from such appliances so as to avoid setting off an alarm due to transient levels emitted from said cooking appliances. In any case, while the alarms are useful for notifying building occupants of the hazard, they do nothing beyond this to ameliorate the situation. The same is true for smoke detectors.
Experts say that American households in general and kitchens in particular are seriously under-ventilated. Many homes are constructed with hoods that do not vent outdoors, and many people do not use their hoods routinely when cooking. They don't like the noise, or the fact that the hoods use extra power and remove conditioned air from the house. When they do use them, they often leave the room and forget to turn them off, which can waste a good deal of additional energy both from the fan itself and the loss of heated or cooled air.
A variety of range hoods have been developed in an attempt to provide ventilation of cooking-related exhaust fumes and other volatile waste products. Different designs are utilized including hoods mounted under cabinets, island hoods and down-drafting hoods that pull fumes from below. The vast majority are manually controlled and will not activate unless the user takes action. A few have implemented fairly simplistic automatic controls such as a single point temperature switch that turns the fan on at maximum speed when excessive temperature, smoke or fumes are detected. Others designed to operate in a commercial environment, vary fan speed in response to effluent factors but cannot turn the fan off due to health code and other restrictions that are unique to a commercial cooking environment. Since, in the commercial environment, the fan is always running at some ventilation level, there is no need for detection of small quantities of hazardous chemicals like carbon monoxide. This means that they can function satisfactorily with a far more simplistic detection scheme than what is required in the residential environment. While these and other devices represent improvements in the art of ventilating heat and fumes generated by cooking, they either do not adequately address the health and safety concerns described above, or they lack the sophistication that will allow them to fit seamlessly into a modern household without being disruptive.
One reason that automatic range hood controls have not yet been popularized is because designing one that works effectively is difficult. Unlike a household furnace, whose thermostat can effectively control the temperature in the house since it controls the source of the heat, a range hood controller has no control over the source of the heat or the fumes or the steam. Therefore it must react without knowledge of what the stove is doing or whether the heat or smoke it just detected is increasing, decreasing or being produced at a steady rate. This is exacerbated by the fact that once the fan is running, it is difficult to tell what is happening below. This makes it particularly problematic to determine when it is time to turn the fan off. Conventional approaches might tend towards a timer-based approach (open loop), which essentially guesses how long the cooking episode will last, and thus runs the risk of either terminating ventilation prematurely, leading to the possibility of spillage of smoke or fumes, or running too long, on the other hand, thereby wasting energy.
Conversely, a closed-loop approach that relies solely on the sensors will likely need to turn the fan off in order to see if more smoke and heat are still coming up. This could lead to a lot of rapid up and down cycling of the fan during the cooking process that, since it is in the kitchen, a place where people often assemble, could be considered objectionable on account of the rapidly changing noise level.
Understanding this shows why a simple temperature set level control like the type used on a furnace, even with hysteresis built in will not be sufficient.
The problem of knowing when to automatically turn a ventilation hood on and off is sometimes addressed by means of a direct electrical connection between the stove and hood, or the use of some external device that could be attached to the stove to determine whether or not gas or electricity is flowing, or even an AC coupling scheme that transmits signals through household wiring. This however, has the drawback of added cost and complexity and the fact that most hoods and stoves are not designed to operate together. Furthermore, even if the amount of gas or electricity could be measured, that would still not directly correlate with the need for ventilation, to be able to distinguish, for example, between a pan full of food that is burning and giving off smoke, and a tea kettle that is simply heating up.
In order to provide optimal performance, it is ideally useful to know precisely, the amount of ventilation required, so as to avoid over-ventilation which can waste a good deal of energy.
For these reasons, plus, for simplicity of installation, a self-contained hood system with a controller that will be able to not only detect the need for ventilation but to determine the amount of ventilation required at any point before, during, or after the cooking process might be desirable.
Such a system would need to address several considerations. First, it would be likely to require some means to determine the dynamic ventilation requirement. This can be accomplished by means of air quality sensors that can assess not only the operating state of the stove, but also the amount of undesirable byproducts being produced. The placement of these sensors can be important in the operation of the hood. Placing them in direct communication with the ventilation air stream provides the most responsive performance, though care would need to be taken to dampen the effect of relatively abrupt changes in temperature or contaminant levels as the fan turns on which might otherwise lead to unstable performance. Response time is also quite important, so that the fan becomes activated before contaminants begin spilling out of the hood.
There is also the question of environmental variability. A robust automatic hood controller would need to function in a wide variety of geographies exhibiting a wide range of background temperature, humidity and contaminant levels. A controller that responds to a fixed preset temperature level or a fixed contaminant level, will perform differently in different environmental settings producing less than ideal results under non-standard conditions.
The above-mentioned considerations suggest the need for a device to address these concerns, that would provide an effective, self-contained, inexpensive, convenient, non-intrusive automated response to the presence of the air quality factors such as heat, humidity, CO and smoke and fumes or other similar hazards in a kitchen as the result of cooking or introduced by some other means, independent of background conditions.
Such a device might also include an alarm feature. There are, of course, various types of smoke and carbon monoxide detectors. These devices are sensitive to the presence of the hazards they are intended to detect and are designed to emit a loud audible alarm when a predetermined level of hazard has been detected. This is, of course, useful and has in many cases saved lives, but there are other cases where they have not been effective. Having the ability to take action beyond emitting an alarm, by, for example, providing ventilation could also prove useful.
In providing this capability in conjunction with a ventilation device that is located in very close proximity to where people are cooking, it might be helpful to be able to automatically adjust the volume level of the alarm so as not to be able to provide the necessary function without being overwhelming.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.